Power measurements in switched mode power supplies

ABSTRACT

A switched mode power supply (SMPS) includes a filter, a power factor correction (PFC) circuit, and a control circuit configured to determine various electrical parameters of the SMPS. In some embodiments, the control circuit is configured to determine a power line frequency and an AC input voltage based on an AC line voltage and an AC neural voltage. In other embodiments, the control circuit is configured to determine an AC input current based on a reactive current flowing through the filter and a PFC AC current. In further embodiments, the control circuit is configured to report a value of an electrical parameter if value is determined to be accurate. Other example switch mode power supplies, control circuits and methods are also disclosed.

FIELD

The present disclosure relates to power measurements in switched modepower supplies.

BACKGROUND

This section provides background information related to the presentdisclosure which is not necessarily prior art.

An AC-DC switched mode power supply (SMPS) commonly includes a filter, apower factor correction (PFC) circuit, and a control circuit. Thecontrol circuit may calculate an input current, an input voltage, aninput power, etc. of the SMPS based on sensed parameters. Typically, theSMPS employs a power-metering chip for measuring input current and inputvoltage, calculating input power, etc.

SUMMARY

This section provides a general summary of the disclosure, and is not acomprehensive disclosure of its full scope or all of its features.

According to one aspect of the present disclosure, a SMPS includes aline rail, a neutral rail, a filter coupled between the line rail andthe neutral rail and having an input for receiving an AC input voltageand an AC input current, an X-capacitance, and an output, a PFC circuitcoupled to the output of the filter and having an input for receiving aPFC AC current, and a control circuit coupled to the PFC circuit. Thecontrol circuit is configured to generate an analog signal representinga difference between an AC line voltage and an AC neutral voltage,compare the analog signal and a defined threshold to determine zerocrossings of the analog signal, determine a frequency of the AC inputvoltage or the AC input current based on at least two of the zerocrossings of the analog signal, determine a reactive current flowingthrough the X-capacitance in the filter based on the determinedfrequency, and determine the AC input current of the SMPS based on thedetermined reactive current and the PFC AC current.

According to another aspect of the present disclosure, a method fordetermining an AC input current of a SMPS is disclosed. The SMPSincludes a line rail, a neutral rail, a filter coupled between the linerail and the neutral rail, and a PFC circuit coupled to the output ofthe filter. The method includes generating an analog signal representinga difference between an AC line voltage and an AC neutral voltage,comparing the analog signal and a defined threshold to determine zerocrossings of the analog signal, determining a frequency of an AC inputvoltage or an AC input current based on at least two of the zerocrossings of the analog signal, determining a reactive current in thefilter based on the determined frequency, and determining the AC inputcurrent of the SMPS based on the determined reactive current and a PFCAC current.

According to another aspect of the present disclosure, a SMPS includes aline rail, a neutral rail, a filter coupled between the line rail andthe neutral rail, and having an input for receiving an AC input voltageand an AC input current, a PFC circuit coupled to the output of thefilter, and a control circuit having a differential amplifier and adigital controller. The differential amplifier is configured to generatean analog signal representing a difference between an AC line voltageand an AC neutral voltage. The digital controller is configured todetermine the AC input voltage and a frequency of the AC input voltageor the AC input current based on the analog signal.

According to another aspect of the present disclosure, a SMPS includes afilter having an input for receiving an AC input current, anX-capacitance, and an output, a PFC circuit coupled to the output of thefilter, and a control circuit coupled to the PFC circuit. The controlcircuit is configured to determine a value of an AC input electricalparameter of the SMPS, estimate a value of the AC input electricalparameter of the SMPS based on a defined efficiency and an output powerof the SMPS, determine an average value of the AC input electricalparameter if a difference between the determined value of the AC inputelectrical parameter and the estimated value of the AC input electricalparameter is less than a defined tolerance threshold, determine anaccuracy of the determined value of the AC input electrical parameterbased on the average value of the AC input electrical parameter, andreport the determined value of the AC input electrical parameter to anexternal device if the accuracy of the determined value of the AC inputelectrical parameter is less than a defined accuracy threshold.

According to another aspect of the present disclosure, a method forreporting an AC input electrical parameter of a SMPS is disclosed. TheSMPS includes a filter and a PFC circuit. The method includesdetermining a value of the AC input electrical parameter of the SMPS,estimating a value of the AC input electrical parameter of the SMPSbased on a defined efficiency and an output power of the SMPS, if adifference between the determined value of the AC input electricalparameter and the estimated value of the AC input electrical parameteris less than a defined tolerance threshold, determining an average valueof the AC input electrical parameter, determining an accuracy of thedetermined value of the AC input electrical parameter based on theaverage value of the AC input electrical parameter, and if the accuracyof the determined value of the AC input electrical parameter is lessthan a defined accuracy threshold, reporting the determined value of theinput electrical parameter to an external device.

According to another aspect of the present disclosure, a SMPS includes aline rail, a neutral rail, a filter coupled between the line rail andthe neutral rail, a PFC circuit coupled to the filter, a DC/DC powercircuit coupled to the PFC circuit, and a control circuit. The filterincludes an input for receiving an AC input voltage and an AC inputcurrent, an X-capacitance, and an output. The PFC circuit includes aninput for receiving a PFC AC current, at least one power switch, and anoutput. The DC/DC power circuit includes at least one power switch and atransformer. The control circuit is coupled to the PFC circuit forcontrolling the at least one power switch of the PFC circuit and to theDC/DC power circuit for controlling the at least one power switch of theDC/DC power circuit. The control circuit includes at least onedifferential amplifier, a primary side digital controller, a secondaryside digital controller, and an isolation device coupled between theprimary side digital controller and the secondary side digitalcontroller. The differential amplifier is configured to generate ananalog signal representing a difference between an AC line voltage andan AC neutral voltage. The primary side digital controller is configuredto determine the AC input voltage based on the analog signal, determinea frequency of the AC input voltage or the AC input current based on theanalog signal, determine a reactive current flowing through theX-capacitance based on the determined frequency, and determine the ACinput current based on the determined reactive current and the PFC ACcurrent.

Further aspects and areas of applicability will become apparent from thedescription provided herein. It should be understood that variousaspects of this disclosure may be implemented individually or incombination with one or more other aspects. It should also be understoodthat the description and specific examples herein are intended forpurposes of illustration only and are not intended to limit the scope ofthe present disclosure.

DRAWINGS

The drawings described herein are for illustrative purposes only ofselected embodiments and not all possible implementations, and are notintended to limit the scope of the present disclosure.

FIG. 1 is a flow diagram of a method for determining an AC input currentof a SMPS according to one example embodiment of the present disclosure.

FIG. 2 is a graph illustrating zero crossings of a signal fordetermining a power line frequency according to another exampleembodiment.

FIG. 3 is a block diagram of a SMPS including a filter, a PFC circuitand a control circuit according to yet another example embodiment.

FIG. 4 is a schematic diagram of a SMPS including a filter, a PFCcircuit, a DC/DC power converter, and a control circuit according toanother example embodiment.

FIG. 5 is a graph illustrating waveforms of an inductor current and aninput current of the SMPS of FIG. 4, according to yet another exampleembodiment.

FIG. 6 is a graph illustrating waveforms of a reactive current and aninput current of the SMPS of FIG. 4, according to another exampleembodiment.

FIG. 7 is a graph illustrating calculated input power values and actualinput power values of a SMPS for determining offset errors and gainerrors of an analog-to-digital converter (ADC) in the control circuit ofFIG. 4, according to yet another example embodiment.

FIG. 8 is a block diagram of a SMPS including a filter, a bridgerectifier, a PFC circuit, a DC/DC power converter, and a control circuitaccording to another example embodiment.

FIG. 9 is a flow diagram of a method for reporting an AC inputelectrical parameter of a SMPS according to yet another exampleembodiment.

FIG. 10 is a flow diagram of a method for calibrating and reporting anAC input power of a SMPS according to another example embodiment.

FIG. 11 is a flow diagram of a method for calibrating and reporting anAC input current of a SMPS according to yet another example embodiment.

Corresponding reference numerals indicate corresponding (but notnecessarily identical) parts and/or features throughout the severalviews of the drawings.

DETAILED DESCRIPTION

Example embodiments are provided so that this disclosure will bethorough, and will fully convey the scope to those who are skilled inthe art. Numerous specific details are set forth such as examples ofspecific components, devices, and methods, to provide a thoroughunderstanding of embodiments of the present disclosure. It will beapparent to those skilled in the art that specific details need not beemployed, that example embodiments may be embodied in many differentforms and that neither should be construed to limit the scope of thedisclosure. In some example embodiments, well-known processes,well-known device structures, and well-known technologies are notdescribed in detail.

The terminology used herein is for the purpose of describing particularexample embodiments only and is not intended to be limiting. As usedherein, the singular forms “a,” “an,” and “the” may be intended toinclude the plural forms as well, unless the context clearly indicatesotherwise. The terms “comprises,” “comprising,” “including,” and“having,” are inclusive and therefore specify the presence of statedfeatures, integers, steps, operations, elements, and/or components, butdo not preclude the presence or addition of one or more other features,integers, steps, operations, elements, components, and/or groupsthereof. The method steps, processes, and operations described hereinare not to be construed as necessarily requiring their performance inthe particular order discussed or illustrated, unless specificallyidentified as an order of performance. It is also to be understood thatadditional or alternative steps may be employed.

When an element or layer is referred to as being “on,” “engaged to,”“connected to,” or “coupled to” another element or layer, it may bedirectly on, engaged, connected or coupled to the other element orlayer, or intervening elements or layers may be present. In contrast,when an element is referred to as being “directly on,” “directly engagedto,” “directly connected to,” or “directly coupled to” another elementor layer, there may be no intervening elements or layers present. Otherwords used to describe the relationship between elements should beinterpreted in a like fashion (e.g., “between” versus “directlybetween,” “adjacent” versus “directly adjacent,” etc.). As used herein,the term “and/or” includes any and all combinations of one or more ofthe associated listed items.

Although the terms first, second, third, etc. may be used herein todescribe various elements, components, regions, layers and/or sections,these elements, components, regions, layers and/or sections should notbe limited by these terms. These terms may be only used to distinguishone element, component, region, layer or section from another region,layer or section. Terms such as “first,” “second,” and other numericalterms when used herein do not imply a sequence or order unless clearlyindicated by the context. Thus, a first element, component, region,layer or section discussed below could be termed a second element,component, region, layer or section without departing from the teachingsof the example embodiments.

Spatially relative terms, such as “inner,” “outer,” “beneath,” “below,”“lower,” “above,” “upper,” and the like, may be used herein for ease ofdescription to describe one element or feature's relationship to anotherelement(s) or feature(s) as illustrated in the figures. Spatiallyrelative terms may be intended to encompass different orientations ofthe device in use or operation in addition to the orientation depictedin the figures. For example, if the device in the figures is turnedover, elements described as “below” or “beneath” other elements orfeatures would then be oriented “above” the other elements or features.Thus, the example term “below” can encompass both an orientation ofabove and below. The device may be otherwise oriented (rotated 90degrees or at other orientations) and the spatially relative descriptorsused herein interpreted accordingly.

Example embodiments will now be described more fully with reference tothe accompanying drawings.

A method for determining an AC input current of a SMPS including afilter and a PFC circuit according to one example embodiment of thepresent disclosure is illustrated in FIG. 1 and indicated generally byreference number 100. As shown in FIG. 1, the method 100 includesgenerating an analog signal representing a difference between an AC linevoltage and an AC neutral voltage in the SMPS in block 102, comparingthe analog signal and a defined threshold to determine zero crossings ofthe analog signal in block 104, determining a power line frequency(e.g., a frequency of an AC input voltage and/or an AC input current)based on at least two of the zero crossings of the analog signal inblock 106, determining a reactive current flowing in the filter based onthe determined frequency in block 108, and determining the AC inputcurrent of the SMPS based on the determined reactive current and a PFCAC current in block 110.

By identifying zero crossings of the analog signal, the power linefrequency of the SMPS may be accurately calculated. This power linefrequency is used in determining the AC input current, as furtherexplained below. As such, precisely determining the power line frequencyensures the determined input current is accurate. Because the inputcurrent is accurately determined, current sensing devices such asconventional power-metering devices (e.g., power meter chips) used tomonitor input parameters such as an AC input current are unnecessary.

As explained above, the AC input current is determined based on the PFCAC current and the reactive current. For example, FIG. 2 illustrates aSMPS 200 including a line rail L, a neutral rail N, a filter 202 coupledbetween the line rail L and the neutral rail N for receiving an AC inputcurrent i_in, and a PFC circuit 204 coupled to an output of the filter202. The filter 202 (e.g., an electromagnetic interference (EMI) filter)includes one or more X-capacitors coupled between the line rail L andthe neutral rail N. For purposes of calculations, the one or moreX-capacitors may be combined into an equivalent X-capacitance C_eq ofthe filter 202. These X-capacitors provide a path for a reactive currenti_c to flow between the line rail L and the neutral rail N. As such, acurrent i_pfc provided to the PFC circuit 204 is not necessary equal tothe AC input current i_in. Therefore, when determining the AC inputcurrent i_in, compensation should be made for the reactive current i_cflowing through the filter's X-capacitors.

Referring back to FIG. 1, the power line frequency may be determinedbased on at least two zero crossings of the analog signal representing adifference between the AC line voltage and the AC neutral voltage. Forexample, FIG. 3 illustrates a graph 300 including an analog signal 302and a square wave signal 304. The analog signal 302 represents adifference between the AC line voltage and the AC neutral voltage asexplained above. In some examples, the analog signal 302 may begenerated with a single differential amplifier, as further explainedbelow.

The square wave signal 304 may be generated based on a comparisonbetween the analog signal 302 and a defined threshold. For example, acomparator may be used to generate the square wave signal 304. In suchexamples, the comparator may output a high or low signal when the analogsignal 302 equals the defined threshold, is greater than the definedthreshold, is less than the defined threshold, etc. After which, thecomparator may be reset. This creates various rising edges and fallingedges of the square wave signal 304.

The defined threshold may be a zero crossing of the analog signal 302.For example, the defined threshold may equal zero. In other examples,the defined threshold may be another suitable positive value if theanalog signal is shifted to prevent the signal from falling below zero.This may be necessary if a digital controller (e.g., digital signalprocessor (DSP)) is used to process the information and calculate thepower line frequency. In the particular example of FIG. 3, the analogsignal is shifted 1.65 V (e.g., half of the 3.3 DSP voltage), andtherefore the defined threshold is 1.65 V.

The rising edges and/or falling edges of the square wave signal 304 maycorrespond to the zero crossings of the analog signal. For example, inthe particular example of FIG. 3, each rising edge and each falling edgeof the square wave signal 304 correspond to one zero crossing (e.g.,1.65 V) of the analog signal. In other examples, only the rising edgesor only the falling edges may correspond to the zero crossings.

In the example of FIG. 3, the power line frequency may be determinedbased on two consecutive zero crossings. For example, when twoconsecutive zero crossings are used to determine the frequency f, a timeinterval (t) between the two consecutive zero crossing points may behalf of the period (T) of main power supply, as shown below in equation(1). Equation (1) may be rearranged into equation (2) to solve for thefrequency (f). In equation (2) above, the time interval (t) may bemeasured, determined, etc. by, for example, an edge interruptionmechanism in a control circuit (e.g., any one of the control circuitdisclosed herein).

$\begin{matrix}{t = {{\frac{1}{2} \times T} = {\frac{1}{2} \times \frac{1}{f}}}} & {{Equation}\mspace{14mu}(1)} \\{f = \frac{1}{2 \times t}} & {{Equation}\mspace{14mu}(2)}\end{matrix}$

In some examples, the power line frequency of a power supply may varyfrom 47 Hz to 63 Hz. This variation in the frequency may have a largeimpact on impedances in the power supply, such as on the X-capacitanceC_eq of the filter 202 in FIG. 2. For example, the capacitive reactanceof the X-capacitance C_eq of FIG. 2 is 1/(2*pi*f*C). This capacitivereactance affects the reactive current i_c. As such, by determining theprecise value of the power line frequency (f), the reactive current i_cmay be accurately calculated (as further explained below). As a result,the input current i_in may be determined with precision.

Additionally, the power line frequency (f) determination explained aboveis adaptive to frequency variations. For example, if the unknown powerline frequency (f) of the input voltage varies, zero crossings of theanalog signal will change accordingly. In turn, the time interval (t)between the two consecutive zero crossing points changes. Thus, even ifthe power line frequency (f) varies (e.g., between 47 Hz and 63 Hz), thefrequency determination scheme explained above may precisely determinethe value of the frequency (f).

The determined input current may be used in a variety of ways. Forexample, the determined input current may be used to calculate otherelectrical parameters (e.g., input power, etc.) of the SMPS. In suchexamples, conventional power-metering devices (e.g., power meter chips)that calculate input parameters are unnecessary. Additionally, thedetermined input current may be periodically, randomly or continuouslyreported to an external device for monitoring purposes. In otherexamples, the determined input current may be used for controlling oneor more power switches in the PFC circuit and/or other power conversioncircuitry in the SMPS. In such examples, the determined input currentmay be used to increase the power factor of the SMPS.

The above methods for determining an AC input current may be implementedin any suitable control circuit including, for example, any one of thecontrol circuits disclosed herein. For example, and as shown in FIG. 2,the SMPS 200 includes a control circuit 206 coupled to the PFC circuit204 for controlling at least one power switch 208 in the PFC circuit204. As shown in FIG. 2, the control circuit 206 receives sensed signals210, 212 representing the AC line voltage and the AC neutral voltage,respectively. In some examples, the control circuit 206 may generate ananalog signal (e.g., the analog signal 302 of FIG. 3) representing adifference between the AC line voltage and the AC neutral voltage, anddetermine an AC input voltage of the SMPS 200 and/or a power linefrequency based on the analog signal. In some instances, the controlcircuit 206 may compare the analog signal and a defined threshold todetermine zero crossings of the analog signal, and then determine thepower line frequency based on at least two of the zero crossings of theanalog signal. In some examples, the control circuit may determine thereactive current i_c flowing through the X-capacitance C_eq based on thedetermined frequency, and determine the AC input current of the SMPS 200based on the determined reactive current i_c and the PFC AC currenti_pfc, as explained above.

The control circuit 206 may include various components for determiningthe power line frequency, the AC input voltage, the AC input currenti_in, etc. In some examples, the control circuit 206 may include one ormore amplifiers, comparators, filters, controllers, etc. for determiningthe AC input current i_in. For example, FIG. 4 illustrates an AC-DC SMPS400 including a control circuit 406 having differential amplifiers 408,410, a comparator 412, filters 414, 416 (e.g., RC filters, etc.) and adigital controller 418 (e.g., a DSP). In other examples, the controlcircuit 406 may include more or less components than is shown in FIG. 4.The control circuit 406 of FIG. 4 is one example implementation of thecontrol circuit 206 of FIG. 2.

In some examples, the differential amplifier 408 may generate an analogsignal representing a difference between an AC line voltage and an ACneutral voltage. In such examples, the digital controller 418 maydetermine an AC input voltage Vin_ac and a power line frequency (e.g.,the frequency of the AC input voltage Vin_ac and/or an AC input currenti_in) based on the analog signal. In some examples, the control circuit406 (e.g., the digital controller 418) may then determine a reactivecurrent i_c, the AC input current i_in, an input power of the SMPS 400,etc.

As shown in FIG. 4, the SMPS 400 further includes a filter 402 and anactive PFC circuit 404 coupled to the output of the filter 402. Asshown, the filter 402 is represented by an equivalent X-capacitance C_eqcoupled across between a line rail L and a neutral rail N. In theparticular example of FIG. 4, the PFC circuit 404 has a boost topology.As such, the PFC circuit 404 includes an inductor L, a power switch Q,and a diode D arranged in a boost configuration. As shown, the powerswitch Q is an N-channel MOSFET. In other examples, another suitabletopology and/or suitable switching device may be employed if desired.

The power switch Q of the PFC circuit 404 may be controlled with a PFCcurrent loop control. For example, the control circuit 406 may receive abulk voltage of the PFC circuit 404 via a voltage divider 424, and aninductor current iL via the differential amplifier 410 and the filter416. The control circuit 406 may then generate a control signal with adriver 426 for controlling the power switch Q.

Additionally, the SMPS 400 includes a DC/DC power converter 420 (e.g., aDC/DC power circuit) coupled to the output of the PFC circuit 404. TheDC/DC power converter 420 may include any suitable converter topologyincluding, for example, a flyback converter, a forward converter (e.g.,a two transistor forward converter), a buck converter, a boostconverter, a bridge converter (e.g., full bridge, half bridge, etc.), aresonant converter (e.g., an LLC converter, etc.), etc. Additionally,the DC/DC power converter 420 may include an isolated converter topology(e.g., having a transformer), or a non-isolated converter topology. Insome examples, the DC/DC power converter 420 may include synchronousrectifiers on the secondary side of an isolation transformer.

Further, the SMPS 400 may include a rectification circuit for rectifyingthe AC input. For example, and as shown in FIG. 4, the SMPS 400 includesa diode bridge rectifier 422 coupled between the filter 402 and the PFCcircuit 404. In some examples, a high frequency filter capacitor C maybe coupled between the rectifier 422 and the PRC circuit 404, as shownin FIG. 4. In other embodiments, other suitable rectification circuitsmay be employed if desired.

The input current i_in may be determined based on the inductor currentiL provided to the PFC circuit 404 and the reactive current i_c in thefilter 402. The input current i_in is expressed as shown in equation (1)below.

i_in(t)=Iac×sin(wt)=iL(t)+ic(t)  Equation (1)

As shown in FIG. 4, an instantaneous value (e.g., an RMS value) of theinductor current iL may be measured based on a voltage drop across ashunt resistor R1. This voltage drop signal is amplified by the singledifferential amplifier 410. Next, the amplified signal is fed to a pinof an ADC in the digital controller 418 via the filter 414. In theparticular example of FIG. 4, the differential amplifier 410 includes anoffset. For example, the differential amplifier 410 may include avoltage divider for shifting (e.g., offsetting) the amplifier's outputto ensure the output is positive.

In such examples, the inductor current iL may be determined based on avoltage (Vil.ADC) sampled by the ADC (e.g., the ADC counter value), andprovided by the differential amplifier 410. For example, the value ofthe ADC after converting the output of the differential amplifier 410may be determined using equation (2) below.

ViL.ADC=(R1×iL×Gi+Voffset)×ADCU  Equation (2)

In equation (2), R1 is the value of the shunt resistor, Gi is the gainof the differential amplifier 410, Voffset is the offset in thedifferential amplifier 410 as explained above, and ADCi is the ADC'sinterrupt bit. The interrupt bit ADCi may be expressed as equation (3)below, where N is the number of bits of the ADC, and Vref is thereference voltage provided to the ADC.

$\begin{matrix}{{ADCi} = \frac{2^{N}}{Vref}} & {{Equation}\mspace{14mu}(3)}\end{matrix}$

The inductor current iL may be calculated by rearranging equation (1),as shown below in equation (4).

$\begin{matrix}{{iL} = {{{{ViL}.{ADC}} \times \frac{Vref}{2^{N}} \times \frac{1}{R\; 1 \times {Gi}}} - \frac{Voffset}{R\; 1 \times {Gi}}}} & {{Equation}\mspace{14mu}(4)}\end{matrix}$

In equation (4), values of the Vref, N, R1, Gi and Voffset are knownbased on the design of the SMPS 400. In such examples, if the ADC is a12 bit ADC (as is typical), the reference voltage Vref is 2.5V, andVoffset/(R1×Gi) equals Ioffset, equation (4) may be simplified toequation (5) below.

$\begin{matrix}{{iL} = {{{{ViL}.{ADC}} \times \frac{2.5}{2^{12}} \times \frac{1}{R\; 1 \times {Gi}}} - {Ioffset}}} & {{Equation}\mspace{14mu}(5)}\end{matrix}$

Equation (5) may be further simplified into equation (6) below. Inequation (6), Ki equals 2.5/2{circumflex over ( )}12*1/Rs*Gi, A equalsViL.ADC, and B equals Ioffset. In such examples, the inductor current iLcan be derived once the ADC counter value ViL.ADC is obtained by thedigital controller 418.

iL=Ki×A−B  Equation (6)

The reactive current i_c may be determined based on the equivalentX-capacitance C_eq, as shown in equation (7) below.

$\begin{matrix}{{{i\_ c}(t)} = {{C\_ eq} \times \frac{{dVc}(t)}{dt}}} & {{Equation}\mspace{14mu}(7)}\end{matrix}$

In equation (7), Vc is the voltage across the equivalent X-capacitanceC_eq, and is determined based on equation (8) below. In equation (8),Vac(t) is the AC main input voltage, Vac is a measured value of the ACinput voltage, and w equals 2×π(pi)×f (frequency).

Vc(t)=Vac(t)=Vac×sin(wt)  Equation (8)

When equations (7) and (8) are combined, the reactive current i_c may beexpressed as equation (9) below.

i_c(t)=C_eq×Vac×w×cos(wt)  Equation (9)

For example, FIGS. 5 and 6 illustrate graphs 500, 600 including variouswaveforms of simulated current in the SMPS 400. Specifically, the graph500 of FIG. 5 includes a current waveform 502 representing the inductorcurrent iL(t), and a current waveform 504 representing the input currenti_in(t). The graph 600 of FIG. 6 includes a current waveform 602representing the reactive current i_c(t), and a current waveform 604representing the input current i_in(t).

The graph 600 shows the impact of the reactive current i_c at a lightload. For example, at a light load (e.g., 20% load and below, etc.), theinput current i_in(t) (waveform 604) and the inductor current iL(t)(e.g. the PFC current) are small. As such, the reactive current i_c(t)(waveform 602) may have a larger impact on the input current i_in(t)than as compared to a larger load, a full load, etc. Thus, if thereactive current i_c(t) cannot be accurately calculated at, for example,a light load, the input current i_in(t) (determined based on thereactive current) may not meet desired accuracy standards.

Referring back to FIG. 4, the control circuit 406 uses the singledifferential amplifier 408 to determine the AC main input voltage andthe frequency (f). For example, and as shown in FIG. 4, the differentialamplifier 408 generates an analog signal representing a differencebetween the AC line voltage and the AC neutral voltage, as explainedherein. This analog signal is provided to the digital controller 418 forobtaining the AC main input voltage. For example, an instantaneous value(e.g., an RMS value) of the AC main input voltage Vac may be determinedbased on equation (10) below.

$\begin{matrix}{{{Vac}.{ADC}} = {\left( {\left( {{Vac} \times \frac{R\; 2}{{R\; 1} + {R\; 2}}} \right) + Z} \right) \times \frac{2^{N}}{Vref}}} & {{Equation}\mspace{14mu}(10)}\end{matrix}$

In equation (10), Vac.ADC represent a voltage (e.g., the analog signal)sampled by the ADC and provided by the differential amplifier 408,R2/(R1+R2) represents a voltage divider for scaling down the mainvoltage to an acceptable voltage level for the digital controller 418, Nis the number of bits of the ADC, and Vref is the reference voltageprovided to the ADC. Additionally, Z represents a voltage shift (e.g.,1.25V) to accommodate the ADC voltage range (e.g., 2.5V).

The control circuit 406 may determine the frequency (f) when obtainingthe AC main input voltage. For example, and as shown in FIG. 4, theanalog signal generated by the differential amplifier 408 is provided tothe comparator 412. The comparator 412 compares the analog signal (e.g.,the analog signal 302 of FIG. 3) to a defined threshold, and generates asquare wave signal (e.g., the square wave signal 304 of FIG. 3) for thedigital controller 418 based on the comparison, as explained above. Thedefined threshold is selected to ensure rising edges and/or fallingedges of the square wave signal correspond to the zero crossings of theanalog signal (and therefore the AC main input voltage). The ADC in thedigital controller 418 then calculates the power line frequency (f)based on the rising edges and falling edges (zero crossings) of theanalog signal, as explained above.

By developing the analog signal (the AC main input voltage) with thesingle differential amplifier 408 and determining precise zero crossingswith the comparator 412, the power line frequency (f) may be accuratelycalculated. For example, and as explained herein, the frequency (f) isdetermined based on zero crossing points of the analog signal (a singlewaveform) generated by the differential amplifier 408. In contrast,conventional approaches determined frequency based on multiplewaveforms. Specifically, conventional approaches determined zerocrossing points of a line voltage signal and zero crossing points of aneutral voltage signal, and then determined the frequency based on bothsets of zero crossing points. As such, any delay between when the linevoltage signal and the neutral voltage signal crosses zero may causeinaccuracies in the determined frequency. However, in the presentdisclosure, the power line frequency (f) may be accurately determinedwithout this delay. In turn, the precise power line frequency (f) may beused to accurately determine the reactive current i_c, as explainedabove.

Additionally, in the particular example of FIG. 4, the AC main inputvoltage and the frequency (0 are determined by using the singledifferential amplifier 408 (e.g., a high impedance differentialamplifier). In such examples, only one port of the ADC in the digitalcontroller 418 may be required to obtain the frequency (f) as comparedto traditional control schemes that measure the AC line voltage and theAC neutral voltage, and require two or more ADC ports.

In some embodiments, the control circuit 406 may determine the inputpower provided to the SMPS 400. For example, the digital controller 418may determine an input power Pin of the SMPS 400 based on the analogsignal and the AC input current. More specifically, the digitalcontroller 418 may calculate the input power Pin by multiplying an RMSvalue of the AC main input voltage Vac calculated in equation (10)above, and an RMS value of the AC input current i_in calculated inequation (1) above. In such examples, the power factor is assumed to bea value near unity (1), such as 0.99.

The calculated input power Pin may be used to calibrate the SMPS 400based on the actual input power. For example, FIG. 7 illustrates a graph700 including multiple values PM1-4 of the calculated input power Pinand multiple values P1-4 of the actual input power at different loads.Specifically, the values PM1, P1 correspond to a 10% load, the valuesPM2, P2 correspond to a 20% load, the values PM3, P3 correspond to a 50%load (half load), and the values PM4, P4 correspond to a 100% load (fullload).

Based on the points of intersection between each correspondingcalculated value and actual value, offset errors and gain errors of theADC in the digital controller 418 may be determined at various loads.For example, the offset error and the gain error may be calculated basedon the values PM1-4, P1-4 corresponding to the 10% load, the 20% load,the 50% load, and the 100% load. For instance, equations (11) and (12)below may be used to determine the offset error and the gain error,respectively, between the 10% load and the 20% load.

$\begin{matrix}{{{Offset}\mspace{14mu}{Error}_{{10\%} - {20\%}}}-=\frac{\left( {P\; 1 \times {PM}\; 1} \right) - \left( {P\; 2 \times {PM}\; 1} \right)}{{P\; 1} - {P\; 2}}} & {{Equation}\mspace{14mu}(11)} \\{\mspace{79mu}{{{Gain}\mspace{14mu}{Error}_{{10\%} - {20\%}}} = {{\left( \frac{{P\; 1} - {P\; 2}}{{{PM}\; 1} - {{PM}\; 2}} \right) - 1}}}} & {{Equation}\mspace{14mu}(12)}\end{matrix}$

Additionally, equations (13) and (14) below may be used to determine theoffset error and the gain error, respectively, between the 50% load andthe 100% load.

$\begin{matrix}{{{Offset}\mspace{14mu}{Error}_{{50\%} - {100\%}}}-=\frac{\left( {P\; 3 \times {PM}\; 4} \right) - \left( {P\; 4 \times {PM}\; 3} \right)}{{P\; 3} - {P\; 4}}} & {{Equation}\mspace{14mu}(13)} \\{\mspace{79mu}{{{Gain}\mspace{14mu}{Error}_{{50\%} - {100\%}}} = {{\left( \frac{{P\; 3} - {P\; 4}}{{{PM}\; 3} - {{PM}\; 4}} \right) - 1}}}} & {{Equation}\mspace{14mu}(14)}\end{matrix}$

The offset error and the gain error calculations may also be applicableto output power of the SMPS 400. For example, a calculated output powerof the SMPS 400 may be used to calibrate the SMPS 400 based on theactual output power. In such examples, equations similar to equations(11)-(14) may be employed to determine the offset error and the gainerror at various loads.

In some examples, the control circuits disclosed herein may report oneor more electrical parameters to an external device. For example, FIG. 8illustrates an AC-DC SMPS 800 including a control circuit 806 having aninterface for communicating with an external device. In the particularexample of FIG. 8, the interface includes a power management bus(PMBus). In other examples, the interface may additionally and/oralternatively include an I-squared-C bus, a universal serial bus (USB),a wire, a connector, a terminal, etc.

As shown in FIG. 8, the SMPS 800 includes the filter 402, the bridgerectifier 422, the PFC circuit 404, and the DC/DC power converter 420 ofFIG. 4. For example, the DC/DC power converter 420 may include at leastone power switch 802 and a transformer 804 coupled to the power switch802. Although the power switch 802 is shown coupled along a high DC railand to a primary winding of the transformer 804, it should be apparentto those skilled in the art that the power switch 802 and/or thetransformer 804 may be coupled in another suitable manner depending on,for example, the topology of the DC/DC power converter 420.

The control circuit 806 of FIG. 8 is similar to the control circuit 406of FIG. 4, but includes additional components for controlling the powerswitch 802 of the DC/DC power converter 420 along with the power switchQ of the PFC circuit 404. For example, the control circuit 806 includesa main voltage conditioning circuit 808, the digital controller 418 ofFIG. 4 (e.g., a primary side digital controller), a secondary sidedigital controller 812, and an opto-coupler 810 coupled between theprimary side digital controller 418 and the secondary side digitalcontroller 812. The main voltage conditioning circuit 808 may include adifferential amplifier (e.g., the differential amplifier 408 of FIG. 4),a comparator (e.g., the comparator 412 of FIG. 4), etc. for developing asignal based on the line and neutral voltages and the power linefrequency, as explained above. Additionally, the digital controller 418may determine the power line frequency, a reactive current in the filter402, an AC input current Iin of the SMPS 800, an AC main voltage Vac, aninput power Pin, etc., as explained above.

The digital controller 812 controls one or more power switches in theDC/DC power converter 420. For example, the digital controller 812receives signals representing an output voltage Vout and an outputcurrent Iout of the DC/DC power converter 420, and then generates one ormore control signals based on the received signals for controlling thepower switch(es) in the DC/DC power converter 420.

Additionally, the digital controller 812 may calculate an output powerPout of the SMPS 800 if desired. In some examples, and as shown in FIG.8, the control circuit 806 may pass the calculated output power Poutfrom the secondary side digital controller 812 to the primary sidedigital controller 418. In such examples, the primary side digitalcontroller 418 may use the output power Pout to estimate the input powerPin (as further explained below), control the power switch Q in the PFCcircuit, etc. In other examples, secondary side digital controller 812may estimate the input power Pin if desired.

The opto-coupler 810 provides isolation in the control circuit 806between primary side control components and secondary side controlcomponents. As shown, signals representing input parameters (e.g., theAC main voltage Vac, the AC input current Iin, the input power Pin,etc.) may be passed from the primary side controller 418 to thesecondary side digital controller 812 via the opto-coupler 810, andsignals representing output parameters (the output power Pout, etc.) maybe passed from the secondary side controller 812 to the primary sidedigital controller 418 via the opto-coupler 810. In some examples, theinput and output parameters may be passed through the opto-coupler 810via a universal asynchronous receiver-transmitter (UART).

One or more of the input and output parameters may be reported to theexternal device via the communication interface. For example, in theparticular example of FIG. 8, one or more of the AC main voltage Vac,the AC input current Iin, the input power Pin, the output voltage Vout,the output current Iout, the output power Pout, etc. may be sent by thesecondary side digital controller 812 to the external device via thePMBus. This allows a user to review and confirm the input and outputparameters of the SMPS 800 are at desired levels, and confirm theaccuracy of calculated values of the parameters. In other examples, theprimary side digital controller 418 may report any one or more of theinput and output parameters to the external device via a communicationinterface.

In other embodiments, it may be desirable to report calculated values ofone or more electrical parameters depending on the accuracy of thecalculated value. For example, FIG. 9 illustrates a method 900 forreporting an AC input electrical parameter of a SMPS including a filterand a PFC circuit. As shown in FIG. 9, the method 900 includescalculating a value of the AC input electrical parameter of the SMPS inblock 902. For example, and as further explained below, the AC inputelectrical parameter may be determined based on, e.g., a reactivecurrent in the filter, a PFC input current, etc.

The method 900 further includes estimating a value of the AC inputelectrical parameter of the SMPS in block 904. The estimated value ofthe AC input electrical parameter may be determined based on knowncharacteristics such as the efficiency, the output power, etc. of theSMPS.

Additionally, the method 900 includes determining an average value ofthe calculated AC input electrical parameter in block 906. For example,the AC input electrical parameter may be averaged over a number ofsamples for a number of AC cycles. Averaging the calculated AC inputelectrical parameter may increase the accuracy of the electricalparameter. In some examples, this step is performed if a differencebetween the calculated value of the AC input electrical parameter andthe estimated value of the AC input electrical parameter is less than adefined tolerance threshold.

The method 900 further includes determining an accuracy of thecalculated value of the AC input electrical parameter in block 908, andreporting the calculated value of the input electrical parameter to anexternal device in block 910. The accuracy of the calculated AC inputelectrical parameter may be based on, for example, the average value ofthe AC input electrical parameter. Additionally, in some examples thecalculated value of the input electrical parameter is reported if theaccuracy of the calculated value of the AC input electrical parameter isless than a defined accuracy threshold.

The AC input electrical parameter of FIG. 9 may be any suitableelectrical parameter in the SMPS such as the AC input current, the inputpower, etc. of the SMPS. For example, FIG. 10 illustrates a method 1000for calibrating (or recalibrating) and reporting the input power of theSMPS.

As shown in FIG. 10, the method 1000 includes calculating an AC inputpower Pin.cal of the SMPS in block 1002 and a DC output power Pout.calof the SMPS in block 1004. For example, the AC input power Pin.cal maybe determined based on the calculated AC input current (e.g., an RMSvalue of the AC input current) and AC input voltage (e.g., an RMS valueof the AC input voltage) as explained above relative to equations (1)and (10). In such examples, the calculated AC input current may be basedon a reactive current in a filter, a PFC current, a power linefrequency, etc. as explained above. The DC output power Pout.cal may bedetermined based on a sensed output voltage Vout and output current Ioutof a DC/DC power converter, as explained above relative to FIG. 8.

Next, the method 1000 includes querying a table in block 1006, andestimating an AC input power Pin.est in block 1008. For example, thetable may include various known efficiency curves based on actualmeasurements. The table may be a lookup table stored in, for example, acontrol circuit implementing the method 1000. The estimated AC inputpower Pin.est may be calculated based on the calculated output powerPout.cal (which is typically more accurate than the calculated inputpower Pin.cal), and the efficiency curves. For example, the estimated ACinput power Pin.est may be calculated based on equation (15) below. Inequation (15), n represents an efficiency of the SMPS, η_(PFC)represents an efficiency of the PFC circuit, η_(DC/DC) represents anefficiency of the DC/DC power converter, etc. at the calculated outputpower Pout.cal.

$\begin{matrix}{{{Pin}.{est}} = {\frac{{Pout}.{cal}}{\eta} = \frac{{Pout}.{cal}}{\eta_{PFC} \times \eta_{{DC}/{DC}}}}} & {{Equation}\mspace{14mu}(15)}\end{matrix}$

The method 1000 further includes determining whether a difference ΔPinbetween the calculated AC input power Pin.cal and the estimated AC inputpower Pin.est is less than a defined tolerance threshold ε in block1010. The defined tolerance threshold ε may be any suitable valuedepending on, for example, the estimated AC input power Pin.est and adesired accuracy of the AC input power Pin.cal. For example, if it isdesirable to have an accuracy within a particular value, the definedtolerance threshold E may be equal to the estimated AC input powerPin.est multiplied by the particular value. For instance, if theestimated AC input power Pin.est is 869 W and it is desirable to have anaccuracy within 2%, the defined tolerance threshold ε may be equal toabout 17 W (869 W*2%).

If it is determined that the difference ΔPin between the calculated ACinput power Pin.cal and the estimated AC input power Pin.est is greaterthan or equal to the defined tolerance threshold ε in block 1010, themethod 1000 returns to calculating the AC input power Pin.cal of theSMPS in block 1002. In such examples, the AC input power Pin.cal may berecalculated in the attempt to determine a more accurate value of the ACinput power Pin.cal. For example, any one of the various parameters usedin calculating the AC input power Pin.cal may change. For instance,parameters such as the reactive current, the AC input current, the powerline frequency, etc. may be recalculated to determine values that aremore accurate. As a result, the AC input current may be determined, andthe AC input power Pin.cal may become more accurate. As such, the ACinput power Pin.cal may be calibrated (or recalibrated) to obtain a moreaccurate value.

If it is determined that the difference ΔPin between the calculated ACinput power Pin.cal and the estimated AC input power Pin.est is lessthan the defined tolerance threshold E in block 1010, an average valueof the AC input power Pin.avg is calculated in block 1012. In someexamples, averaging the value of the AC input power Pin.cal may improvethe accuracy. For example, the average value of the AC input powerPin.avg may be calculated based on equation (16) below. In equation(16), N may represent any suitable value including, for example, thenumber of samples for a number of AC cycles. In some examples, it isdesirable to increase the value of N to achieve a more accurate averagedvalue of the AC input power Pin.cal.

$\begin{matrix}{{{Pin}.{avg}} = \frac{\sum{{Pin}.{cal}}}{N}} & {{Equation}\mspace{14mu}(16)}\end{matrix}$

Next, the method 1000 includes determining whether an accuracy of thecalculated AC input power Pin.cal is less than a defined accuracythreshold Acc_threshold in block 1014. This determination may be madebased on the averaged AC input power Pin.avg, as shown in equation (17)below.

$\begin{matrix}{\frac{{{{Pin}.{cal}} - {{Pin}.{avg}}}}{{Pin}.{avg}} < {Acc}_{threshold}} & {{Equation}\mspace{14mu}(17)}\end{matrix}$

The defined accuracy threshold Acc_threshold may be any suitable valuebased on, for example, design parameters, etc. In some examples, thedefined accuracy threshold Acc_threshold may depend on the load coupledto the SMPS. For example, the defined accuracy threshold Acc_thresholdmay be 2% for loads ranging between 20-100% load, etc. In otherexamples, the defined accuracy threshold Acc_threshold may be 5% forlighter loads (e.g., loads ranging between 10-20% load, etc.).

If it is determined that the accuracy of the calculated AC input powerPin.cal is greater than or equal to the defined accuracy threshold inblock 1014, the method 1000 returns to calculating (or recalculating)the AC input power Pin.cal of the SMPS in block 1002 in the attempt todetermine a more accurate value of the AC input power Pin.cal, asexplained above. In such examples, the AC input power Pin.cal may becalibrated (or recalibrated) to obtain a more accurate value. If,however, the determined accuracy of the calculated AC input powerPin.cal is less than the defined accuracy threshold in block 1014, thecalculated AC input power Pin.cal may be reported to an external devicein block 1016. For example, the calculated AC input power Pin.cal may bereported via a PMBus as explained above.

In other examples, the AC input electrical parameter of FIG. 9 may bethe AC input current. For example, FIG. 11 illustrates a method 1100 forcalibrating (or recalibrating) and reporting the AC input current of theSMPS. The method 1100 of FIG. 11 is substantially similar to the method1000 of FIG. 10, but refers to the AC input current.

For example, and as shown in FIG. 11, the method 1100 includescalculating an AC input current Iin.cal of the SMPS in block 1102 and aDC output power Pout.cal of the SMPS in block 1104. The AC input currentIin.cal may be determined based on a reactive current, a PFC current, apower line frequency, etc. as explained above.

The method 1100 then includes querying a table in block 1106, andestimating an AC input current Iin.est in block 1108. As explainedabove, the table (e.g., a stored lookup table) may include various knownefficiency curves based on actual measurements. The estimated AC inputcurrent Iin.est in FIG. 11 may be calculated based on the calculatedoutput power Pout.cal, the efficiency curves, and an AC main voltageVac. For example, the estimated AC input current Iin.est may becalculated based on equation (17) below.

$\begin{matrix}{{{Vac} \times {{Iin}.{est}}} = {{{Pin}.{est}} = {\frac{{Pout}.{cal}}{\eta} = \frac{{Pout}.{cal}}{\eta_{PFC} \times \eta_{{DC}/{DC}}}}}} & {{Equation}\mspace{14mu}(17)}\end{matrix}$

Next, the method 1100 includes determining whether a difference ΔIinbetween the calculated AC input current Iin.cal and the estimated ACinput current Iin.est is less than a defined tolerance threshold ε inblock 1110. For example, the defined tolerance threshold ε may bedetermined in a similar manner as explained above relative to the inputpower's tolerance threshold ε.

If it is determined that the difference ΔIin between the calculated ACinput current Iin.cal and the estimated AC input current Iin.est isgreater than or equal to the defined tolerance threshold ε in block1110, the method 1100 returns to calculating (or recalculating) the ACinput current Iin.cal in block 1102 in the attempt to determine a moreaccurate value of the AC input current Iin.cal. In such examples, the ACinput current Iin.cal may be calibrated (or recalibrated) and/ordetermined to obtain a more accurate value if more accurate values ofthe reactive current, the PFC current, the power line frequency, etc.are obtained. If, however, it is determined that the difference ΔIinbetween the calculated AC input current Iin.cal and the estimated ACinput current Iin.est is less than the defined tolerance threshold ε inblock 1110, an average value of the AC input current Iin.avg iscalculated in block 1112. This may improve the accuracy of the AC inputcurrent Iin.cal. For example, the average value of the AC input currentIin.avg may be calculated based on equation (17) below. In equation(17), N may represent the number of samples for a number of AC cycles,as explained above.

$\begin{matrix}{{{Iin}.{avg}} = \frac{\sum{{Pin}.{cal}}}{N}} & {{Equation}\mspace{14mu}(17)}\end{matrix}$

The method 1100 further includes determining whether an accuracy of thecalculated AC input current Iin.cal is less than a defined accuracythreshold Acc_threshold in block 1114. The defined accuracy thresholdAcc_threshold relating to the calculated AC input current Iin.cal may beany suitable value such as 2%, 5%, etc., as explained above relative tothe defined accuracy threshold relating to the AC input power. Theaccuracy of the calculated AC input current Iin.cal is determined basedon the averaged AC input power Iin.avg, as shown in equation (18) below.

$\begin{matrix}{\frac{{{{Iin}.{cal}} - {{Iin}.{avg}}}}{{Iin}.{avg}} < {Acc}_{threshold}} & {{Equation}\mspace{14mu}(18)}\end{matrix}$

If the accuracy of the calculated AC input current Iin.cal is greaterthan or equal to the defined accuracy threshold in block 1114, themethod 1100 returns to calculating (or recalculating) the AC inputcurrent Iin.cal in block 1102 in the attempt to determine a moreaccurate value of the AC input current Iin.cal (e.g., recalibration), asexplained above. If, however, the determined accuracy of the calculatedAC input current Iin.cal is less than the defined accuracy threshold inblock 1114, the calculated AC input power Iin.cal may be reported to anexternal device in block 1116 via, for example, a PMBus as explainedabove.

The methods 900, 1000, 1100 for calibrating (or recalibrating) and/orreporting an AC input electrical parameter may be implemented by anysuitable control circuit including, for example, any one of the controlcircuits disclosed herein. In some examples, some or all portions of themethods may be implemented with one or more of the digital controllersdisclosed herein (e.g., the primary side digital controller, thesecondary side digital controller, etc.) may be used. Additionally, themethods for calibrating (or recalibrating) and/or reporting an AC inputelectrical parameter may be implemented in the control circuit inconjunction with the methods for determining an AC input current. Inother examples, the methods for recalibrating and/or reporting an ACinput electrical parameter (and not the methods for determining an ACinput current) may be implemented in the control circuit, or vice-versa.

The control circuits disclosed herein may include an analog controlcircuit, a digital control circuit, or a hybrid control circuit (e.g., adigital control unit and an analog circuit). The digital controlcircuits may be implemented with one or more types of digital controlcircuitry. For example, the digital control circuits each may include adigital controller such as a digital signal controller (DSC), a DSP, amicrocontroller unit (MCU), a field-programmable gate array (FPGA), anapplication-specific IC (ASIC), etc. As such, any one of the controlmethods disclosed herein may be at least partially (and sometimesentirely) performed by a digital controller.

If, for example, the control circuit is a digital control circuit, thecontrol circuit may be implemented with one or more hardware componentsand/or software. For example, instructions for performing any one ormore of the features disclosed herein may be stored in and/ortransferred from a non-transitory computer readable medium, etc. to oneor more existing digital control circuits, new digital control circuits,etc. In such examples, one or more of the instructions may be stored involatile memory, nonvolatile memory, ROM, RAM, one or more hard disks,magnetic disk drives, optical disk drives, removable memory,non-removable memory, magnetic tape cassettes, flash memory cards,CD-ROM, DVDs, cloud storage, etc.

Portions of the control circuits may be on the secondary side of anisolation barrier if, for example, the corresponding power circuitincludes an isolation transformer. In such cases, control signal(s) fromthe control circuits may cross the isolation barrier (e.g., via one ormore isolation devices such as isolation transformers, opto-couplers,etc.) to control power switches on the primary side of the powercircuit, as shown in FIG. 8.

In addition, the control methods disclosed herein may be repeated asdesired. For example, the control circuits may be able to successivelyperform the methods as desired and/or if applicable.

The teachings disclosed herein may be applicable in any suitable SMPShaving one or more power circuits. In some examples, the teachings maybe implemented in at least part of a front-end AC-DC distributed powersupply. In such examples, the power supply may receive an AC inputvoltage ranging between 90-264 VAC at power line frequency rangingbetween 47-63 Hz, and provide a regulated 12 VDC output or anothersuitable output voltage. For example, the power supply may have anoutput power rating of 800 W at 12V/66.7 A, 1800 W at 12V/147.5 A, 2000W at 12V/163.9 A, 2400 W at 12V/196.7 A, and/or another suitable powerrating. In some examples, the power supply may include redundantarchitectures, and provide a single output. The power supply may beparticularly useful in server applications, storage applications (e.g.,database applications, cloud hosting applications, etc.), networkingapplications, etc.

By employing the control methods disclosed herein, an AC main voltagemay be developed to include precise zero crossings without a delay thatis typically seen in conventional approaches when sampling line andneutral voltages. As a result, an accurate value of the power linefrequency may be obtained from the zero crossings, and an accurate inputcurrent determination may be achieved based on the power line frequency.In some examples, the AC main voltage may be developed using a singledifferential amplifier. In such examples, only one port of an ADC in adigital controller (if employed) may be required as compared to multipleports in conventional approaches.

Additionally, the control methods may provide a solution for measuringinput power without relying on power-metering devices (e.g., power meterchips) as in conventional approaches. As a result, costs are reduced,board space is increased, etc. as compared to conventional approaches.Thus, the teachings disclosed herein may provide a low cost, compactSMPS design.

Further, the control methods may provide a solution for calibrating (orrecalibrating) input parameters such as an AC input current, inputpower, etc. to improve accuracy of the parameters. If the accuracy of aparameter is adequate, the parameter may be reported to an externaldevice if desired. The calibrating (or recalibrating) of inputparameters may be performed while the SMPS is operating (e.g., on-line).As such, calibrations may be based on real-time calculations.

Also disclosed are the following numbered clauses:

1. A switched mode power supply (SMPS) comprising:

a line rail and a neutral rail;

a filter coupled between the line rail and the neutral rail, the filterincluding an input for receiving an AC input voltage and an AC inputcurrent, an X-capacitance, and an output;

a power factor correction (PFC) circuit coupled to the output of thefilter, the PFC circuit including an input for receiving a PFC ACcurrent; and

a control circuit coupled to the PFC circuit, the control circuitconfigured to generate an analog signal representing a differencebetween an AC line voltage and an AC neutral voltage, compare the analogsignal and a defined threshold to determine zero crossings of the analogsignal, determine a frequency of the AC input voltage or the AC inputcurrent based on at least two of the zero crossings of the analogsignal, determine a reactive current flowing through the X-capacitancein the filter based on the determined frequency, and determine the ACinput current of the SMPS based on the determined reactive current andthe PFC AC current.

2. The SMPS of any preceding claim wherein the control circuit includesa differential amplifier configured to generate the analog signal.

3. The SMPS of any preceding claim wherein the control circuit includesa digital controller configured to receive the analog signal anddetermine an input power of the SMPS based on the analog signal and theAC input current.

4. The SMPS of any preceding claim wherein the control circuit includesa comparator configured to compare the analog signal and the definedthreshold, and generate a square wave signal having rising edges andfalling edges based on the comparison between the analog signal and thedefined threshold, and wherein the rising edges or the falling edgescorrespond to the zero crossings.

5. The SMPS of any preceding claim wherein the control circuit isconfigured to determine an input power of the SMPS, determine anaccuracy of the input power based on an average value of the inputpower, and report the input power to an external device if the accuracyis less than a defined accuracy threshold.

6. The SMPS of any preceding claim wherein the determined value of theinput power is a first determined value of the input power, and whereinthe control circuit is configured to determine another value of theinput power if the accuracy of the first determined value of the inputpower is greater than or equal to the defined accuracy threshold.

7. The SMPS of any preceding claim wherein the control circuit isconfigured to determine an accuracy of the determined AC input currentbased on an average value of the AC input current, and report thedetermined AC input current to an external device if the accuracy isless than a defined accuracy threshold.

8. The SMPS of any preceding claim wherein the determined value of theAC input current is a first determined value of the AC input current,and wherein the control circuit is configured to determine another valueof the AC input current if the accuracy of the first determined value ofthe AC input current is greater than or equal to the defined accuracythreshold.

9. A SMPS comprising:

a filter including an input for receiving an AC input current, anX-capacitance, and an output;

a PFC circuit coupled to the output of the filter; and

a control circuit coupled to the PFC circuit, the control circuitconfigured to determine a value of an AC input electrical parameter ofthe SMPS, estimate a value of the AC input electrical parameter of theSMPS based on a defined efficiency and an output power of the SMPS,determine an average value of the AC input electrical parameter if adifference between the determined value of the AC input electricalparameter and the estimated value of the AC input electrical parameteris less than a defined tolerance threshold, determine an accuracy of thedetermined value of the AC input electrical parameter based on theaverage value of the AC input electrical parameter, and report thedetermined value of the AC input electrical parameter to an externaldevice if the accuracy of the determined value of the AC inputelectrical parameter is less than a defined accuracy threshold.

10. The SMPS of any preceding claim wherein the AC input electricalparameter is an AC input current or an AC input power of the SMPS.

11. The SMPS of any preceding claim wherein the control circuit isconfigured to determine a reactive current in the filter and a PFCcurrent provided to the PFC circuit, and determine the value of the ACinput electrical parameter based on the reactive current and the PFCcurrent.

12. The SMPS of any preceding claim wherein the control circuit isconfigured to determine a frequency of the AC input current, anddetermine the reactive current based on the frequency of the AC inputcurrent.

13. The SMPS of any preceding claim wherein the control circuit isconfigured to determine the frequency of the AC input current bygenerating an analog signal representing a difference between an AC linevoltage in the SMPS and an AC neutral voltage in the SMPS, comparing theanalog signal and a defined threshold to determine zero crossings of theanalog signal, and determining the frequency of the AC input current ofthe SMPS based on the zero crossings of the analog signal.

14. The SMPS of any preceding claim wherein the determined value of theAC input electrical parameter is a first determined value of the ACinput electrical parameter, and wherein the control circuit isconfigured to determine another value of the AC input electricalparameter if the difference between the first determined value of the ACinput electrical parameter and the estimated value of the AC inputelectrical parameter is greater than or equal to the defined tolerancethreshold.

15. The SMPS of any preceding claim wherein the determined value of theAC input electrical parameter is a first determined value of the ACinput electrical parameter, and wherein the control circuit isconfigured to determine another value of the AC input electricalparameter if the accuracy of the first determined value of the AC inputelectrical parameter is greater than or equal to the defined accuracythreshold.

16. A SMPS comprising:

a line rail and a neutral rail;

a filter coupled between the line rail and the neutral rail, the filterincluding an input for receiving an AC input voltage and an AC inputcurrent;

a PFC circuit coupled to the output of the filter; and

a control circuit including a differential amplifier and a digitalcontroller, the differential amplifier configured to generate an analogsignal representing a difference between an AC line voltage and an ACneutral voltage, and the digital controller configured to determine theAC input voltage and a frequency of the AC input voltage or the AC inputcurrent based on the analog signal.

17. The SMPS of any preceding claim wherein the control circuit includesa comparator coupled between the differential amplifier and the digitalcontroller, wherein the comparator is configured to compare the analogsignal and a defined threshold to determine zero crossings of the analogsignal, and wherein the digital controller is configured to determinethe frequency of the AC input voltage or the AC input current based onat least two of the zero crossings of the analog signal.

18. The SMPS of any preceding claim wherein the comparator is configuredto generate a square wave signal having rising edges and falling edgesbased on the comparison between the analog signal and the definedthreshold, and wherein the rising edges or the falling edges correspondto the zero crossings.

19. The SMPS of any preceding claim wherein the at least two of the zerocrossings of the analog signal are two consecutive zero crossings of theanalog signal.

20. The SMPS of any preceding claim wherein the filter includes anX-capacitance, and wherein the digital controller is configured todetermine a reactive current flowing through the X-capacitance based onthe determined frequency.

21. The SMPS of any preceding claim wherein the PFC circuit includes aninput for receiving a PFC AC current, and wherein the digital controlleris configured to determine the AC input current based on the determinedreactive current and the PFC AC current.

22. The SMPS of any preceding claim wherein the digital controller isconfigured to determine an accuracy of the determined AC input currentbased on an average value of the AC input current, and report thedetermined AC input current to an external device if the accuracy isless than a defined accuracy threshold.

23. The SMPS of any preceding claim wherein the determined value of theAC input current is a first determined value of the AC input current,and wherein the control circuit is configured to determine another valueof the AC input current if the accuracy of the first determined value ofthe AC input current is greater than or equal to the defined accuracythreshold.

24. The SMPS of any preceding claim wherein the digital controller isconfigured to receive the analog signal and determine an input power ofthe SMPS based on the determined AC input voltage signal and thedetermined AC input current.

25. The SMPS of any preceding claim wherein the digital controller isconfigured to determine an accuracy of the input power based on anaverage value of the input power, and report the input power to anexternal device if the accuracy is less than a defined accuracythreshold.

26. The SMPS of any preceding claim wherein the determined value of theinput power is a first determined value of the input power, and whereinthe control circuit is configured to determine another value of theinput power if the accuracy of the first determined value of the inputpower is greater than or equal to the defined accuracy threshold.

27. A SMPS comprising:

a line rail and a neutral rail;

a filter coupled between the line rail and the neutral rail, the filterincluding an input for receiving an AC input voltage and an AC inputcurrent, an X-capacitance, and an output;

a PFC circuit coupled to the output of the filter, the PFC circuitincluding an input for receiving a PFC AC current, at least one powerswitch, and an output;

a DC/DC power circuit coupled to the output of the PFC circuit, theDC/DC power circuit including at least one power switch and atransformer; and

a control circuit coupled to the PFC circuit for controlling the atleast one power switch of the PFC circuit and to the DC/DC power circuitfor controlling the at least one power switch of the DC/DC powercircuit, the control circuit including at least one differentialamplifier, a primary side digital controller, a secondary side digitalcontroller, and an isolation device coupled between the primary sidedigital controller and the secondary side digital controller, thedifferential amplifier configured to generate an analog signalrepresenting a difference between an AC line voltage and an AC neutralvoltage, and the primary side digital controller configured to determinethe AC input voltage based on the analog signal, determine a frequencyof the AC input voltage or the AC input current based on the analogsignal, determine a reactive current flowing through the X-capacitancebased on the determined frequency, and determine the AC input currentbased on the determined reactive current and the PFC AC current.

28. The SMPS of any preceding claim wherein the control circuit includesa comparator coupled between the differential amplifier and the primaryside digital controller, wherein the comparator is configured to comparethe analog signal and a defined threshold to determine zero crossings ofthe analog signal, and wherein the primary side digital controller isconfigured to determine the frequency of the AC input voltage or the ACinput current based on at least two of the zero crossings of the analogsignal.

29. The SMPS of any preceding claim wherein the comparator is configuredto generate a square wave signal having rising edges and falling edgesbased on the comparison between the analog signal and the definedthreshold, and wherein the rising edges or the falling edges correspondto the zero crossings.

30. The SMPS of any preceding claim wherein the at least two of the zerocrossings of the analog signal are two consecutive zero crossings of theanalog signal.

31. The SMPS of any preceding claim wherein the primary side digitalcontroller is configured to determine the AC input current based on thedetermined reactive current and the PFC AC current.

32. The SMPS of any preceding claim wherein the primary side digitalcontroller is configured to determine an accuracy of the determined ACinput current based on an average value of the AC input current, andwherein the secondary side digital controller is configured to reportthe determined AC input current to an external device if the accuracy isless than a defined accuracy threshold.

33. The SMPS of any preceding claim wherein the determined value of theAC input current is a first determined value of the AC input current,and wherein the primary side digital controller is configured todetermine another value of the AC input current if the accuracy of thefirst determined value of the AC input current is greater than or equalto the defined accuracy threshold.

34. The SMPS of any preceding claim wherein the primary side digitalcontroller is configured to receive the analog signal and determine aninput power of the SMPS based on the determined AC input voltage signaland the determined AC input current.

35. The SMPS of any preceding claim wherein the primary side digitalcontroller is configured to determine an input power of the SMPS, anddetermine an accuracy of the input power based on an average value ofthe input power, and wherein the secondary side digital controller isconfigured to report the input power to an external device if theaccuracy is less than a defined accuracy threshold.

36. The SMPS of any preceding claim wherein the determined value of theinput power is a first determined value of the input power, and whereinthe primary side digital controller is configured to determine anothervalue of the input power if the accuracy of the first determined valueof the input power is greater than or equal to the defined accuracythreshold.

The foregoing description of the embodiments has been provided forpurposes of illustration and description. It is not intended to beexhaustive or to limit the disclosure. Individual elements or featuresof a particular embodiment are generally not limited to that particularembodiment, but, where applicable, are interchangeable and can be usedin a selected embodiment, even if not specifically shown or described.The same may also be varied in many ways. Such variations are not to beregarded as a departure from the disclosure, and all such modificationsare intended to be included within the scope of the disclosure.

1. A switched mode power supply (SMPS) comprising: a line rail and a neutral rail; a filter coupled between the line rail and the neutral rail, the filter including an input for receiving an AC input voltage and an AC input current, an X-capacitance, and an output; a power factor correction (PFC) circuit coupled to the output of the filter, the PFC circuit including an input for receiving a PFC AC current; and a control circuit coupled to the PFC circuit, the control circuit configured to generate an analog signal representing a difference between an AC line voltage and an AC neutral voltage, compare the analog signal and a defined threshold to determine zero crossings of the analog signal, determine a frequency of the AC input voltage or the AC input current based on at least two of the zero crossings of the analog signal, determine a reactive current flowing through the X-capacitance in the filter based on the determined frequency, and determine the AC input current of the SMPS based on the determined reactive current and the PFC AC current.
 2. The SMPS of claim 1 wherein the control circuit includes a differential amplifier configured to generate the analog signal.
 3. The SMPS of claim 1 wherein the control circuit includes a digital controller configured to receive the analog signal and determine an input power of the SMPS based on the analog signal and the AC input current.
 4. The SMPS of claim 1 wherein the control circuit includes a comparator configured to compare the analog signal and the defined threshold, and generate a square wave signal having rising edges and falling edges based on the comparison between the analog signal and the defined threshold, and wherein the rising edges or the falling edges correspond to the zero crossings.
 5. A SMPS comprising: a filter including an input for receiving an AC input current, an X-capacitance, and an output; a PFC circuit coupled to the output of the filter; and a control circuit coupled to the PFC circuit, the control circuit configured to determine a value of an AC input electrical parameter of the SMPS, estimate a value of the AC input electrical parameter of the SMPS based on a defined efficiency and an output power of the SMPS, determine an average value of the AC input electrical parameter if a difference between the determined value of the AC input electrical parameter and the estimated value of the AC input electrical parameter is less than a defined tolerance threshold, determine an accuracy of the determined value of the AC input electrical parameter based on the average value of the AC input electrical parameter, and report the determined value of the AC input electrical parameter to an external device if the accuracy of the determined value of the AC input electrical parameter is less than a defined accuracy threshold.
 6. The SMPS of claim 5 wherein the AC input electrical parameter is an AC input current or an AC input power of the SMPS.
 7. A SMPS comprising: a line rail and a neutral rail; a filter coupled between the line rail and the neutral rail, the filter including an input for receiving an AC input voltage and an AC input current; a PFC circuit coupled to the filter; and a control circuit including a differential amplifier and a digital controller, the differential amplifier configured to generate an analog signal representing a difference between an AC line voltage and an AC neutral voltage, and the digital controller configured to determine the AC input voltage and a frequency of the AC input voltage or the AC input current based on the analog signal.
 8. The SMPS of claim 7 wherein the control circuit includes a comparator coupled between the differential amplifier and the digital controller, wherein the comparator is configured to compare the analog signal and a defined threshold to determine zero crossings of the analog signal, and wherein the digital controller is configured to determine the frequency of the AC input voltage or the AC input current based on at least two of the zero crossings of the analog signal.
 9. A SMPS comprising: a line rail and a neutral rail; a filter coupled between the line rail and the neutral rail, the filter including an input for receiving an AC input voltage and an AC input current, an X-capacitance, and an output; a PFC circuit coupled to the output of the filter, the PFC circuit including an input for receiving a PFC AC current, at least one power switch, and an output; a DC/DC power circuit coupled to the output of the PFC circuit, the DC/DC power circuit including at least one power switch and a transformer; and a control circuit coupled to the PFC circuit for controlling the at least one power switch of the PFC circuit and to the DC/DC power circuit for controlling the at least one power switch of the DC/DC power circuit, the control circuit including at least one differential amplifier, a primary side digital controller, a secondary side digital controller, and an isolation device coupled between the primary side digital controller and the secondary side digital controller, the differential amplifier configured to generate an analog signal representing a difference between an AC line voltage and an AC neutral voltage, and the primary side digital controller configured to determine the AC input voltage based on the analog signal, determine a frequency of the AC input voltage or the AC input current based on the analog signal, determine a reactive current flowing through the X-capacitance based on the determined frequency, and determine the AC input current based on the determined reactive current and the PFC AC current.
 10. The SMPS of claim 9 wherein the control circuit includes a comparator coupled between the differential amplifier and the primary side digital controller, wherein the comparator is configured to compare the analog signal and a defined threshold to determine zero crossings of the analog signal, and wherein the primary side digital controller is configured to determine the frequency of the AC input voltage or the AC input current based on at least two consecutive zero crossings of the analog signal.
 11. The SMPS of claim 10 wherein the comparator is configured to generate a square wave signal having rising edges and falling edges based on the comparison between the analog signal and the defined threshold.
 12. The SMPS of claim 8 wherein the comparator is configured to generate a square wave signal having rising edges and falling edges based on the comparison between the analog signal and the defined threshold, and wherein the rising edges or the falling edges correspond to the zero crossings.
 13. The SMPS of claim 7 wherein the filter includes an X-capacitance, and wherein the digital controller is configured to determine a reactive current flowing through the X-capacitance based on the frequency of the AC input voltage or the AC input current, and determine the AC input current based on the reactive current.
 14. The SMPS of claim 13 wherein the digital controller is configured to determine an accuracy of the determined AC input current based on an average value of the AC input current, and report the determined AC input current to an external device if the accuracy is less than a defined accuracy threshold.
 15. The SMPS of claim 14 wherein the determined value of the AC input current is a first determined value of the AC input current, and wherein the digital controller is configured to determine another value of the AC input current if the accuracy of the first determined value of the AC input current is greater than or equal to the defined accuracy threshold.
 16. The SMPS of claim 13 wherein the digital controller is configured to determine an input power of the SMPS based on the determined AC input voltage signal and the determined AC input current, determine an accuracy of the input power based on an average value of the input power, and report the input power to an external device if the accuracy is less than a defined accuracy threshold.
 17. The SMPS of claim 16 wherein the determined value of the input power is a first determined value, and wherein the digital controller is configured to determine another value of the input power if the accuracy of the first determined value is greater than or equal to a defined accuracy threshold.
 18. The SMPS of claim 5 wherein the control circuit is configured to determine a reactive current in the filter and a PFC current provided to the PFC circuit and determine the value of the AC input electrical parameter based on the reactive current and the PFC current.
 19. The SMPS of claim 18 wherein the control circuit is configured to determine a frequency of the AC input current, and determine the reactive current based on the frequency of the AC input current.
 20. The SMPS of claim 5 wherein the determined value of the AC input electrical parameter is a first determined value, and wherein the control circuit is configured to determine another value of the AC input electrical parameter if the difference between the first determined value and the estimated value of the AC input electrical parameter is greater than or equal to the defined tolerance threshold, or if the accuracy of the first determined value is greater than or equal to the defined accuracy threshold. 